Cells adapt to the levels of O2 by regulating gene expression. The regulation of this response is complex, likely because O2 is required for several cellular processes, like aerobic respiration and biosynthesis of essential molecules. In humans, the response to O2 levels can be hijacked to promote tumorigenesis or can aid recovery after adverse cardiovascular episodes. The yeast S. cerevisiae is an advantageous model organism for studying the O2 response because S. cerevisiae is genetically tractable, shares many signaling genes with human cells, and has a robust response to O2 levels. The S. cerevisiae response is complex as there are hundreds of genes that change expression in response to O2, with varying magnitude and kinetics. Many signaling pathways, comprising 19 total genes, have been shown to participate in this regulation. The primary goals of the current study are to place all genes into independent signaling pathways and then determine how the pathways contribute to the entire gene expression response. In order to achieve these goals, the signaling genes will each be deleted to create several yeast strains. To test the effect of the deletions, these strains will be tested for cellular phenotypes and for gene expression in response to changing O2 levels. It is expected that these different strains will have differing phenotypes depending on the signaling pathway that is disrupted in the strain. Also, the strains will be subject to RNA-Seq experiments which will monitor how yeast genes respond to changing O2 levels. Extensive data is generated from RNA-Seq experiments, and the data will be analyzed using extensive statistical approaches. These experiments will help delineate O2 signaling pathways and determine how they contribute to the overall response to O2 levels. In addition, the study will attempt to recapitulate the gene expression response to O2 levels by experimentally manipulating O2-dependent metabolic pathways. The signaling pathways described above do not appear to directly sense O2 but instead sense at least three metabolic changes that occur when O2 levels change. These metabolic changes will be simultaneously induced and gene expression monitored over time using RNA-Seq. Together, our experiments will help uncover the vast signaling network that mediates the gene expression response to O2 levels. Importantly, this work will contribute to our understanding of eukaryotic cellular signaling, a process that is disrupted in many human diseases.